Signal Measurement on Component Carriers in Wireless Communication Systems

ABSTRACT

A method in a wireless communication terminal including generating a first averaged signal measurement on a first carrier frequency, wherein the first averaged signal measurement is based on a first averaging period, producing a first filter output based on the first averaged signal measurement weighted by a first weight, generating a second averaged signal measurement on the first carrier frequency, wherein the second averaged signal measurement is based on a second averaging period, and producing a second filter output based on the first filter output and based on the second averaged signal measurement weighted by a second weight, wherein the first weight is less than the second weight if the second averaging period is greater than a threshold.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wireless communications and,more particularly, to measurement of component carriers in wirelesscommunication systems.

BACKGROUND

Carrier aggregation (CA) will be used in future 3GPP LTE wirelesscommunication networks to provide improved data rates to users. Carrieraggregation includes transmitting data to or receiving data from userequipment (UE) on multiple carrier frequencies (component carriers). Thewider bandwidth enables higher data rates.

A UE can generally be configured with a set of component carriers (CCs).Specifically, the UE is configured with a cell on each componentcarrier. Some of these cells may be activated. The activated cells canbe used to send and receive data (i.e., the activated cells can be usedfor scheduling). The UE has up-to-date system information for allconfigured cells. Therefore, after a cell has been configured, it can bequickly activated. Thus, when there is a need for aggregating multipleCCs (e.g., upon the occurrence of a large burst of data), the networkcan activate configured cells on one or more of the CCs. Generally,there is a designated primary cell (Pcell) on a CC that is referred toas the primary CC, which is always activated. The other configured cellsare referred to as Scells (and the corresponding CCs are referred to assecondary CCs).

The maintenance of a configured CC set in addition to an activated CCset enables battery conservation in the UE while providing CCs that canbe activated when necessary, for example, when there is a substantialamount of data to be transmitted.

It is expected that multiple carriers will be activated only when thereis a substantial amount of data to be transmitted. This implies that CCswill remain in the configured but deactivated state for extended timeperiods. It is essential to perform RRM measurements of cells on thedeactivated CCs so that the appropriate CCs (and cells) can beactivated. Performing measurements of multiple CCs requires the UE tooperate its RF frontend at a higher bandwidth (in the case of intra-bandaggregation), or to use an alternate transceiver for measurements. Bothof these options cause significant power consumption in the UE.Performing frequent measurements of CCs with activated cells does notresult in substantial additional power consumption since the UE isrequired to be able to receive control channels and data channels fromthe activated cells anyway (and therefore the RF front end needs to beable to receive the activated CCs). A UE is generally not expected toreceive control and data channels on deactivated secondary cells. UEsare configured with secondary cells in the deactivated state forextended time periods. Cumulatively, measurements of cells on secondaryCCs can consume large amounts of power. Thus it is generally consideredbeneficial to control the rate at which measurements of cells onsecondary CCs are performed to minimize power consumption. That is, itis beneficial to perform measurements of cells on deactivated secondaryCCs less frequently than measurements of cells on the primary CC andcells on activated secondary CCs.

The various aspects, features and advantages of the invention willbecome more fully apparent to those having ordinary skill in the artupon careful consideration of the following Detailed Description thereofwith the accompanying drawings described below. The drawings may havebeen simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary wireless communication system employingcarrier aggregation.

FIG. 2 illustrates the actual conditions experienced by the UE in FIG.1.

FIG. 3 illustrates apparent radio conditions experienced by a UE in FIG.1 making measurements on CC2 at a lower measurement rate than theprimary cell CC1.

FIG. 4 illustrates a process flow diagram.

FIG. 5 illustrates more accurate radio conditions experienced by the UEin FIG. 1 making measurements on CC2 at a measurement rate higher thanthe lower measurement rate of FIG. 3.

FIG. 6 illustrates another process flow diagram.

FIG. 7 illustrates averaging Layer 1 measurements and generating Layer 3filtered measurements based on the Layer 1 measurements.

DETAILED DESCRIPTION

In FIG. 1, a wireless communication system 100 comprises one or morefixed base infrastructure units 101, 102 forming a network distributedover a geographical region for serving remote units in the time and/orfrequency and/or spatial domain. A base unit may also be referred to asan access point, access terminal, base, base station, NodeB, enhancedNodeB (eNodeB), Home NodeB (HNB), Home eNodeB (HeNB), Macro eNodeB(MeNB), Donor eNodeB (DeNB), relay node (RN), femtocell, femto-node,network node or by other terminology used in the art. The one or morebase units each comprise one or more transmitters for downlinktransmissions and one or more receivers for uplink transmissions. Thebase units are generally part of a radio access network that includesone or more controllers communicably coupled to one or morecorresponding base units. The access network is generally communicablycoupled to one or more core networks, which may be coupled to othernetworks like the Internet and public switched telephone networks amongothers. These and other elements of access and core networks are notillustrated but are known generally by those having ordinary skill inthe art.

In FIG. 1, the one or more base units serve a number of remote units,for example, remote unit 103, within a corresponding serving area, forexample, a cell or a cell sector, via a wireless communication link. Theremote units may be fixed or mobile. The remote units may also bereferred to as subscriber units, mobiles, mobile stations, mobile units,users, terminals, subscriber stations, user equipment (UE), userterminals, wireless communication devices, relay node, or by otherterminology used in the art. The remote units also comprise one or moretransmitters and one or more receivers. In FIG. 1, the base units andremote unit communicates in the time and/or frequency and/or spatialdomain. Sometimes the base unit is referred to as a serving or connectedor anchor cell for the remote unit. The remote units may alsocommunicate with the base unit via a relay node.

In one implementation, the wireless communication system is compliantwith the 3GPP Universal Mobile Telecommunications System (UMTS) LTEprotocol, also referred to as EUTRA or 3GPP LTE or some later generationthereof, wherein the base unit transmits using an orthogonal frequencydivision multiplexing (OFDM) modulation scheme on the downlink and theuser terminals transmit on the uplink using a single carrier frequencydivision multiple access (SC-FDMA) scheme. The instant disclosure isparticularly relevant to 3GPP LTE Release 8 (Rel-8), 3GPP LTE Release 9(Rel-9) and LTE Release 10 (Rel-10) and possibly later evolutions, butmay also be applicable to other wireless communication systems. Moregenerally the wireless communication system may implement some otheropen or proprietary communication protocol, for example, IEEE 802.16(d)(WiMAX), IEEE 802.16(e) (mobile WiMAX), among other existing and futureprotocols. The disclosure is not intended to be implemented in anyparticular wireless communication system architecture or protocol. Thearchitecture may also include the use of spreading techniques such asmulti-carrier CDMA (MC-CDMA), multi-carrier direct sequence CDMA(MC-DS-CDMA), Orthogonal Frequency and Code Division Multiplexing(OFCDM) with one or two dimensional spreading. The architecture in whichthe features of the instant disclosure are implemented may also be basedon simpler time and/or frequency division multiplexing/multiple accesstechniques, or a combination of these various techniques. In alternateembodiments, the wireless communication system may utilize othercommunication system protocols including, but not limited to, TDMA ordirect sequence CDMA. The communication system may be a Time DivisionDuplex (TDD) or Frequency Division Duplex (FDD) system.

In aggregated carrier (AC) systems, a User Equipment (UE) can receiveand transmit control and data signaling on multiple component carriers(CCs). In FIG. 1, for example, the UE 103 is configured for carrieraggregation and receives from base station 101 a first component carrier(CC1) and a second component carrier (CC2) wherein CC1 is a primary cell(Pcell) and CC2 is a secondary cell (Scell). Initially, the UE maycommunicate with the network by receiving only a single CC (Primary orAnchor CC). In some implementations, the network sends a configurationmessage (SI configuration message) to the UE on the primary CC withsystem information (SI) corresponding to other CCs on which the networkmay schedule the UE. The SI typically includes CC specific informationthat the UE is required to store in order to communicate with thenetwork on other CCs. The SI can include CC specific information such asCC carrier frequency, downlink (DL) bandwidth, number of antennas,downlink reference signal power, uplink (UL) power control parametersand other information that does not change frequently. In someaggregated carrier systems, base station sends the SI configurationmessage to the UE using Radio Resource Configuration (RRC) signaling,since the SI does not change frequently and the payload associated withthe SI configuration is relatively large. Upon receipt of the SIconfiguration, the UE stores the SI for other CCs but continues tocommunicate with the network by only receiving the primary CC. The otherCCs for which the UE has received SI and the primary CC constitute theUE's “configured CC set”.

Performing measurements of cells on deactivated secondary CCs lessfrequently than measurements of cells on primary CC can reduce powerconsumption. However, having different measurement periods can lead toincorrect mobility decisions at the network. In FIG. 1 for example, theUE 103 is connected to eNB1 and is configured with CC1 as a primary cell(PCell) and CC2 as a secondary cell (Scell). The UE is moving towardseNB2. If the Scell is deactivated (CC2 deactivated), the measurementrate on CC2 is less than the rate on CC1. For example, the measurementperiod for the primary cell may be 200 ms and the measurement period forthe secondary cell may be 1600 ms. In FIG. 1, an inter-eNB handovershould be triggered when CC1 from eNB2 102 is better than the primarycell on eNB1 101 (based on an A3 event measurement report). FIG. 2illustrates the actual radio conditions experienced by the UE in FIG. 1.However, the different measurement periods for the primary cell andsecondary cell on eNB 101 lead to a different view of the radioconditions at the UE as illustrated in FIG. 2. FIG. 3 illustrates Layer3 (L3) filtered measurements at the UE. Since the measurements of thesecondary cell are occurring less frequently, the secondary cellmeasurements as observed by the UE lag the actual radio conditionsexperienced by the UE. Since the UE includes in measurement reports tothe base station L3 filtered measurements of the secondary cell, the UEwill report that the secondary cell is better than the primary cell asshown in FIG. 3. This result may cause the eNB1 101 to attempt a primarycell change instead of an inter-eNB handover. An Inter-eNB handover ismore appropriate since signal levels of CC1 and CC2 on eNB1 are actuallyless than CC1 on eNB2. Furthermore, a primary cell change on eNB1 couldfail since the CC2 signal is lower than the reported measurement andanother handover or primary cell change would be required. Similarly,the different measurement periods can also cause unnecessary inter-eNBhandovers when a primary cell change is needed. In the carrieraggregation context, the problem occurs only with deactivated secondarycells. If the secondary cell is activated, the measurements occur at thesame rate as the primary cell. However, since the eNB does not knowexactly when a handover will be required, it is not practical topre-activate the secondary cell. Besides, such an approach would defeatthe purpose of activation and deactivation.

Although the problem is described above in the context of carrieraggregation, similar or related issues can occur in other scenarios. Forexample, coexistence of multiple radios in the UE (in-devicecoexistence) can in some cases lead to similar measurement relatedproblems. Consider the case where the UE has an LTE transceiver and aWiFi transceiver wherein WiFi transmissions by the UE can impact the LTEreception at the UE and LTE transmission by the UE can impact the WiFireception at the UE. Specifically, when WiFi transmission activity isstarted, the measurements on the LTE side see a sudden and significantimpact.

According to a first aspect of the disclosure illustrated in the processflow diagram 400 of FIG. 4, a wireless communication device performsmeasurements of a first serving cell on a first carrier frequency at afirst rate at 410. At 420, the UE determines whether a signal level of asecond serving cell on a second carrier frequency is below a threshold.In one embodiment, the threshold is a secondary serving cell measurementthreshold signaled to the UE by the base station. In other embodiments,the threshold is stored locally or is obtained from some other source.At 430, the UE performs measurements of the first serving cell at asecond rate if the signal level of the second serving cell is below thethreshold. In one instantiation, the rate of measurements of thesecondary serving cell on the second carrier frequency (and, ifnecessary, other cells on the second carrier frequency) increase whenthe signal measured on the primary serving cell is below the threshold.In some embodiments, the measurements performed on the carrierfrequencies are filtered, for example, by a layer 3 (L3) filteringprocess implemented using an infinite impulse response filter or othersuitable filter.

The UE generally comprises a controller coupled to a wirelesstransceiver wherein the controller is configured to perform measurementson the carrier frequencies as described above. The measurementfunctionality performed by the controller may be implemented by adigital processor that executes software or firmware stored on a memorydevice. Similarly, the controller may perform the filteringfunctionality and other functions described herein by executing softwareor firmware. Alternatively the functionality of the UE may be performedby equivalent hardware or by a combination of hardware and software.

In one implementation, the UE is configured for carrier aggregation andthe first carrier frequency is a deactivated carrier and the secondcarrier frequency is a primary carrier frequency. According to thisimplementation, the UE increases the rate at which measurements are madeon the deactivated carrier when the signal on the primary carrier fallsbelow the threshold to more accurately assess radio conditions to whichthe UE is subject. In some implementations, the eNB configures the UEfor carrier aggregation on a primary serving cell on a first carrierfrequency and on a secondary serving cell on a second carrier frequency.As suggested above, the eNB may also determine a secondary serving cellmeasurement threshold to the wireless communication terminal. The eNBmay signal the secondary serving cell measurement threshold to thewireless communication terminal. Thus the UE is provided a primary cellsignal threshold below which measurements of cells on deactivatedsecondary CCs is performed more frequently. For example, referring tothe above scenario, if the UE observes that the primary cell signal isabove the threshold, the UE performs measurements of deactivatedsecondary cell with a relatively long measurement period of 1600 ms toreduce power consumption. When the UE observes that the primary cellsignal drops below the threshold, the UE performs measurements of thedeactivated secondary cell with a measurement period of 480 ms.Alternatively, other measurement periods may also be used.

In another implementation, the UE increases the rate at whichmeasurements are made on the deactivated carrier when the differencebetween the signal on the primary carrier and a signal on anothercarrier rises above a threshold. In some implementations, the eNBconfigures the UE for carrier aggregation on a primary serving cell on afirst carrier frequency and on a secondary serving cell on a secondcarrier frequency. The eNB may also configure a measurement reportingoffset, so that the wireless communication terminal reports measurementsif the difference between the signal level of a cell other than theprimary serving cell and the signal level of the primary cell is higherthan the measurement reporting offset. For example, the UE is configuredwith an A3 measurement event, the event set to trigger when a neighborcell signal is higher than the primary serving cell signal by more thanthe measurement reporting offset. The UE reports measurements when theA3 measurement event is triggered. In addition to reportingmeasurements, the UE performs measurements of cells on deactivatedsecondary CCs more frequently. For example, referring to the abovescenario, if the UE observes that the neighbor cell signal is not higherthan the signal of the primary cell by the measurement reporting offset,the UE performs measurements of deactivated secondary cell with arelatively long measurement period, for example, 1600 ms, to reducepower consumption. When the UE observes that the neighbor cell signal ishigher than the signal of the primary cell by at least the measurementreporting offset, the UE performs measurements of the deactivatedsecondary cell with a measurement period, for example 480 ms.Alternatively, other measurement periods may also be used.

FIG. 5 illustrates the effect of applying the second measurement rate tothe first serving cell, which corresponds to the deactivated carrier inthe aggregated carrier implementation. The more accurate radioconditions (illustrated in FIG. 5) produced using the second measurementrate indicate that the UE should perform an inter-base station handoverfrom eNB1 to eNB2, rather than an intra-base station handover suggestedby the radio conditions measured at the lower rate (as illustrated inFIG. 3). In some implementations, the eNB commands the UE to perform thehandover as described further below, but more generally the handoverdecision may be made autonomously by the UE.

In other implementations, the UE could be a multimode device, forexample, a WiFi enabled LTE device. In this implementation, the UE canperform measurements of one or more of the serving cells more frequentlybased on WiFi activity being initiated or based on some other criteria.

The base station also comprises a controller coupled to a wirelesstransceiver wherein the controller is configured to perform the variousfunctions described herein including configuring the UE for aggregatedcarrier operation and transmission of the threshold to the UE inembodiments for implementations that require it, receipt and processingof measurement reports from the UE, handover analyses and commandtransmission, among other functions performed by the base station.Alternatively the functionality of the eNB may be performed byequivalent hardware or by a combination of hardware and software.

In FIG. 4, at 440, in some embodiments the UE reports information basedon at least some of the measurements to a first base station. In theaggregated carrier implementation above, for example, the information isbased on at least the measurements performed on the first serving cellat the second rate, since these measurements more accurately depict theradio conditions experienced by the UE. In some embodiments, themeasurements performed on the first serving cell are filtered asdescribed above and the UE reports the filtered measurements to the eNBor base station. In other implementations however, the UE may choose toselectively not report some measurements, filtered or otherwise, a basestation. Such embodiments include those where the UE makes handoverdecisions autonomously or where the UE provides handover assistanceinformation to the base station based on the measurements.

In response to sending a measurement report to the eNB, the UE mayreceive a handover command from eNB. Generally, the handover command maybe for an intra-base-station handover or for an inter-base-stationhandover. An inter-base-station handover is a handover from a first basestation to a second base station serving a different coverage area thanthat of the first base station, for example, from eNB1 to eNB2 inFIG. 1. In one embodiment, an intra-base-station handover is a change inprimary serving cell. In FIG. 1, for example, the deactivated secondarycell CC2 could be made the primary serving cell in an intra-base-stationhandover in response to receiving the handover command. Further, anintra-base-station handover can include a change of primary cell from afirst cell of the base station on a first frequency to a second cell ofthe same base station on a second frequency, wherein the second cell isserved by a remote antenna or a remote radio head that is communicablycoupled to the base station. Remote antennas and remote radio heads aredifferent from base stations in that they transmit and receive RFsignals, but do not have most or all of the higher layer functionalityassociated with a base station such as scheduling, medium accesscontrol, connectivity to neighboring base stations etc. For suchfunctionality, the remote antennas and remote radio heads may rely onthe associated base station.

According to another aspect of the disclosure, the UE provides thenetwork information indicating that certain secondary cell measurementsare not reliable. For example, the UE can mark some of the reportedmeasurements as “not reliable”. Alternatively, the UE can omitmeasurements that are not reliable. The UE can determine the reliabilityof the secondary cell measurements in various ways, some examples ofwhich are described below. In one embodiment, the UE can consider the L3filtered measurements to be unreliable if the variance of L1measurements (on which the L3 filtering measurements are based) in ameasurement period is higher than a specified threshold. For example, ifthe difference between the highest L1 measurement and the lowest L1measurement sample exceeds a threshold. In another embodiment, themeasurements to be reported to the eNB may be considered unreliable ifeither the L3 filter measurements or the L1 measurements on which the L3filter measurements are based are older than a specified duration. Thissolution can also be applied to resolve measurements related issues in amulti-mode UE having multiple radio transceivers. For example, if the UEis equipped with a WiFi transceiver, the UE can experience a much lowermeasurements when WiFi transmission is occurring. In such a situation,the UE can mark measurements as unreliable or omit them if WiFi activityis ongoing when the measurements are performed.

According to another aspect of the disclosure illustrated in the processdiagram of FIG. 6, a wireless communication terminal generates a firstaveraged signal measurement on a first carrier frequency, wherein thefirst averaged signal measurement is based on a first averaging periodat 620. At 620, the UE produces a first filter output based on the firstaveraged signal measurement weighted by a first weight. At 630, the UEgenerates a second averaged signal measurement on the first carrierfrequency, wherein the second averaged signal measurement is based on asecond averaging period. At 640, the UE produces a second filter outputbased on the first filter output and based on the second averaged signalmeasurement weighted by a second weight, wherein the first weight isless than the second weight if the second averaging period is greaterthan a threshold.

Generally, the UE produces a third filter output subsequent to producingthe second filter output wherein the third filter output is based on thefirst weight or at least a weight different than the second weight. Thusthe second weight is used only for one or more filter cycles with theeffect of diminishing the impact of older filter outputs on the mostrecent filter output to provide the eNB with a more accurate indicationof the radio conditions experienced by the UE.

In some implementations, the UE receives a message from an eNB orderingthe UE to perform the signal measurements on the first carrier frequencyusing the second averaging period, as described further below. Accordingto this implementation, the wireless communication infrastructureentity, or eNB, transmits a signal measurement averaging period for afirst carrier frequency, wherein the signal measurement averaging periodis transmitted to a wireless communication terminal configured foraggregated carrier operation. As suggested above, the eNB receives afilter output from the UE, wherein the filter output is generated basedon a weighted signal measurement on the first carrier frequency, thesignal measurement is averaged over the signal measurement averagingperiod, and the weight is dependent on the signal measurement averagingperiod. After making a handover decision based on the filter outputreceived, the eNB may transmit a handover command to the UE as discussedfurther below.

In a more particular implementation, the UE produces the first filteroutput using a first filter coefficient and the UE produces the secondfilter output using a second filter coefficient if the second averagingperiod is greater than the threshold, wherein the second filtercoefficient is different than the first filter coefficient. In oneembodiment, the first filter output and second filter output areproduced using an infinite impulse response filter, although othersuitable filters may be used in other embodiments. In one embodiment,the first averaged signal measurement and the second averaged signalmeasurement are averaged layer 1 signal measurements, and the first andsecond filter outputs are layer 3 filtered measurements.

In one application, the second filter coefficient has a value thatnegates the first filter output component of the second filter output.More generally however the first filter output need not be negatedentirely. Generally, the UE adjusts L3 filter coefficient to ensure thatmore recent measurements are weighted more heavily. One example of L3filtering is based on the following IIR filter:

F _(n)=(1−a)·F_(n-1) +a·M _(n),

Where F_(n) is the new filtered measurement, F_(n-1) is the previousfiltered measurement and M_(n) is the new L3 measurement, anda=1/(2^((k/4))), where k is the filter coefficient. Thus the UE can usethe following techniques to ensure more recent measurements are weightedmore heavily than less recent measurements. For example, when the UE isconfigured with a secondary cell measurement period that is larger thanthe primary measurement period, the UE can select a larger value of ‘a’(i.e., choose a smaller value of k) for filtering of secondary cellmeasurements than that used for primary cell measurement filtering. Whenthe UE notices that the latest (or latest n) secondary cell (Scell)measurement is much higher than the previous measurements, the UE usesan ‘a’ value of 1 to remove the effects of previous measurements fromthe filter for one or more L3 filter iterations. This effectivelyamounts to resetting the filter. Subsequently the UE can resume using adefault or other optimized normal value of ‘a’.

In some situations, it may be beneficial to use an ‘a’ value of greaterthan 1 to apply a higher weight to the most recent measurements. Thiscan serve as a faster trigger for certain actions in the UE. Forexample, using an ‘a’ greater than 1 can cause the L3 filteredmeasurement to meet some measurement reporting criteria and hence causethe UE to transmit a measurement report to the base station sooner thanit would with ‘a=1’.

FIG. 7 illustrates Layer 1 (L1) signal measurements (M_(n-1)) averagedover a first measurement averaging period on a carrier frequency and thecorresponding generation of a Layer 3 filter output (F_(n-1)) based onthe averaged L1 signal measurement (M_(n-1)) and based on a priorfiltered output (F_(n-2)) wherein a weighting factor is applied to thefilter output (F_(n-1)) and the averaged signal measurements (M_(n-1)).Also illustrated are L1 signal measurements (M_(n)) averaged over asecond measurement average period and the corresponding generation of aLayer 3 filter output (F_(n)) based on the averaged L1 signalmeasurement (M_(n)) and based on the prior filtered output (F_(n-1))wherein a different weighting factor is applied to the prior filteroutput (F_(n-1)) and the averaged signal measurement (M_(n)) such thatthe prior filter output is negated or weighted less than the averagedsignal measurement (M_(n)). After at least one iteration using thesecond measurement averaging period and the different weighting factor,L1 measurements revert to using the first measurement averaging periodand a weighting factor that weights prior L3 filter outputs more heavilythan does the second weighting factor.

In some embodiments, the UE reports the second filter output to aserving base station, which may use the report to make a handoverdecision. Thus in some instances, the UE receives a handover commandfrom the serving base station in response to the report. The handovermay be an intra-base-station handover or an inter-base-station handover.If the handover command is for an inter-base-station handover, the UEhands over to a second base station in a location different than theserving base station in response to receiving the command. Inembodiments where the wireless communication terminal is configured forcarrier aggregation and wherein the first carrier frequency is adeactivated carrier, the first serving cell may be configured as theprimary serving cell in response to receiving the handover command.

As suggested above, this embodiment can be applied to resolvemeasurements related issues in a multi-mode UE having multiple radiotransceivers, each of the transceivers supporting different radiotechnologies or similar radio technologies in different bands of thewireless spectrum. For example, if the UE is equipped with a WiFitransceiver, when the UE transmits WiFi signals, the UE can experience asudden decrease in measurements. In such a situation, the UE can use ahigher value of “a” (weight the more recent measurements more heavily)when WiFi activity is ongoing. The UE can also reset the filter bysetting a=1 when WiFi activity is initiated. This can provide a moreaccurate view of the radio conditions when transmission of WiFi signalsis started. After the WiFi activity ends, the UE can revert to using alower value of ‘a’.

According to another aspect of the disclosure, a wireless communicationbase station, or eNB, configures a wireless communication terminal tooperate on a first serving cell on a first carrier frequency and on asecond serving cell on a second carrier frequency. Such a configurationmay be for carrier aggregation. The base station also configures thewireless communication terminal to use a first measurement period forthe first serving cell and a second measurement period for the secondserving cell. For example, the eNB in FIG. 1 configures a measurementperiod on the deactivated secondary cell CC2 that is considerably longerthan the measurement period on the primary cell CC1. When the basestation determines that a signal level at the wireless communicationterminal of the first serving cell is below a threshold, the basestation configures the wireless communication terminal to use a thirdmeasurement period for the second serving cell.

Such a determination may be made by the base station based on one ormore measurement reports sent from the UE to the eNB. For example, theUE may be configured with periodical radio resource measurement (RRM)reporting. If a measurement report indicates that the primary cell dropsbelow a threshold, the eNB can consider the primary cell signal to bedeteriorating and reconfigures the measurement period for thedeactivated cell as indicated above. The UE may be configured with eventbased RRM measurement reporting (e.g., A3 event) for the primary cell,such that the reporting occurs well before a handover is necessary. Forthis embodiment, a very conservative A3 offset is used. If a measurementreport is triggered based on this event, the eNB can use the report asan indication that the primary cell signal is deteriorating andreconfigure the measurement period of the secondary as indicated above.The eNB may also observe a channel quality indication (CQI) of theprimary cell dropping below a threshold and based on this assume thatthe primary cell signal is deteriorating. It can then reconfigure themeasurement period as indicated above.

As mentioned above, the solutions above can be applied to resolvemeasurements related issues in a multi-mode UE having multiple radiotransceivers, each of the transceivers supporting different radiotechnologies or similar radio technologies in different bands of thewireless spectrum. For example, the network can configure more frequentmeasurements in response to an indication from the UE that WiFi activityhas been/will be initiated.

In other embodiments, the base station can select values of a filtercoefficient to signal to the terminal. The base station can selectvalues of the filter coefficient based on interference reported by theUE. For example, the UE reports measurements to the base station, themeasurements indicating interference. If the interference is higher thana threshold, the base station can select a filter coefficient thatresults in a higher weight for the more recent measurements.Alternatively, the base station can select values of the filtercoefficient based on another RAT. For example, the base station canreceive an indication from the UE that a transceiver for another RAT isactive at the UE. The base station can then select a filter coefficientsuited to perform more accurate measurements taking one or more of thefollowing criteria into account: activity on the other RAT, transmissionfrequency of the other RAT and characteristics of the other RAT.

Although the solutions are described in terms of radio resourcemanagement (RRM) measurements, the same principles can be applied tochannel state information (CSI) measurements. This can be especiallyuseful in obtaining reliable measurements in multi-mode UEs havingmultiple radio transceivers. For example, the UE can perform morefrequent measurements and reporting of channel quality indication (CQI)when WiFi activity is initiated. The UE can also mark some CQImeasurements as unreliable or omit them if WiFi activity is ongoing.Furthermore, the UE can use different filtering/averaging of CQImeasurements when WiFi activity is initiated.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession and enabling those ofordinary skill to make and use the same, it will be understood andappreciated that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the inventions,which are to be limited not by the exemplary embodiments but by theappended claims.

1. A method in a wireless communication terminal, the method comprising:generating a first averaged signal measurement on a first carrierfrequency, wherein the first averaged signal measurement is based on afirst averaging period; producing a first filter output based on thefirst averaged signal measurement weighted by a first weight; generatinga second averaged signal measurement on the first carrier frequency,wherein the second averaged signal measurement is based on a secondaveraging period; and producing a second filter output based on thefirst filter output and based on the second averaged signal measurementweighted by a second weight, wherein the first weight is different fromthe second weight if the second averaging period is greater than athreshold.
 2. The method of claim 1 wherein the first weight is lessthan the second weight if the second averaging period is greater thanthe threshold.
 3. The method of claim 1 further comprising producing athird filter output subsequent to producing the second filter outputwherein the third filter output is based on the first weight.
 4. Themethod of claim 1 further comprising reporting the second filter outputto a serving base station.
 5. The method of claim 3, receiving ahandover command from the serving base station in response to thereporting.
 6. The method of claim 4 further comprising handing over to asecond base station serving a different coverage area than the servingbase station in response to receiving the handover command.
 7. Themethod of claim 5, wherein a first serving cell on the first carrierfrequency is a deactivated serving cell, the method further comprisingconfiguring the first serving cell as a primary serving cell in responseto receiving the handover command.
 8. The method of claim 1 furthercomprising: producing the first filter output by using a first filtercoefficient; producing the second filter output using a second filtercoefficient if the second averaging period is greater than thethreshold, wherein the second filter coefficient is different than thefirst filter coefficient.
 9. The method of claim 1 wherein the secondfilter coefficient has a value that negates the first filter outputcomponent of the second filter output.
 10. The method of claim 8,wherein the first averaged signal measurement and the second averagedsignal measurement are averaged layer 1 signal measurements, and whereinthe first filter output and the second filter output are layer 3filtered measurements.
 11. The method of claim 1, wherein the firstfilter output and second filter output are infinite impulse responsefilter outputs.
 12. The method of claim 1, wherein the wirelesscommunication terminal is configured for carrier aggregation, andwherein the first carrier frequency is a deactivated carrier.
 13. Themethod of claim 1 further comprising receiving a message ordering theterminal to perform the signal measurements on the first carrierfrequency using the second averaging period.
 14. A method in a wirelesscommunication infrastructure entity, the method comprising: transmittinga signal measurement averaging period for a first carrier frequency, thesignal measurement averaging period is transmitted to a wirelesscommunication terminal configured for aggregated carrier operation,receiving a filter output from the wireless communication terminal, thefilter output generated based on a weighted signal measurement on thefirst carrier frequency, wherein the signal measurement is averaged overthe signal measurement averaging period and wherein the weight isdependent on the signal measurement averaging period; and transmitting ahandover command to the wireless communication terminal based on thefilter output received from the wireless communication terminal.
 15. Themethod claim 15 wherein a longer signal measurement averaging periodcorresponds to a higher weight.